Backported datamap cache hotfix

[TheAndrewJackson]

Closes #3213

Code Changes

• Create new mergeColumns function that handles combining the cached columns with the new columns
• Invalidate the Datamap RTK cache when custom fields are created, edited, and deleted

Steps to Confirm

• Visit the datamap page so the column settings get cached
• Go create a new custom field
• create a system and populate the custom field with data
• visit the datamap table and open the settings modal. The new custom field should be in the listed columns. NOTE: it won't show up if no system is using the column
• Go back and edit the name of the custom field
• Visit the datamap table again and check the settings modal. The column should be in the modal with the new name. It will most likely be at the bottom. That is expected.

Pre-Merge Checklist

• All CI Pipelines Succeeded
• Documentation:
  • documentation complete, PR opened in fidesdocs
  • documentation issue created in fidesdocs
• Issue Requirements are Met
• Relevant Follow-Up Issues Created
• Update CHANGELOG.md
• For API changes, the Postman collection has been updated

Description Of Changes

This fixes the same issue that #3211 fixed. The fix was duplicated because the recent work with the RTK APIs conflicted with what was needed in the release branch. The RTK API update was great for this btw @allisonking. It helped a lot with invalidating the Datamap cache when custom fields are updated.

[cypress]

Passing run #1792 ↗︎

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Details:

Merge 5a79965 into b5b1649...
Project: fides	Commit: f26e3808e1 ℹ️
Status: Passed	Duration: 00:49 💡
Started: May 5, 2023 9:43 PM	Ended: May 5, 2023 9:44 PM

_{This comment has been generated by cypress-bot as a result of this project's GitHub integration settings.}

[allisonking]

yay, those tests look great, thanks for adding them!